1. Field of the Invention
The present invention relates to a method for treating retinal diseases, and more particularly a method for treating diseases caused by light-induced retinal degeneration.
2. Description of the Related Art
Retinal diseases include non-specific retinitis, specific retinitis, proliferating retinitis, retinal periphlebitis, central angiospastic retinitis, exudative retinitis, circinate retinitis, solar retinitis, etc. Aggravation and the onset of these diseases are said to be related to optical disorders of the retina, which disorders are considered to be caused by the generation of superoxides or peroxidation of lipids.
A basic fibroblast growth factor (bFGF) is a member of a family of heparin-binding growth factors. This growth factor exhibits a variety of physiological activities in accelerating the proliferation of fibloblasts, proliferating endothelial cells, and serving as a nerve nutrition factor (Science, Vol. 233, 545-548 (1986). bFGF is also known to suppress retinal disorders of animals caused by light (Proc. Natl. Acad. Sci. U.S.A., Vol., 89, pp 11249-11253 (1992)). Midkine (MK), which was found by Muramatsu et al., is one of a number of factors constituting a new family exhibiting heparin-binding properties. It has also been reported to have a variety of physiological activities which makes it serve as a nerve nutrition factor and a differentiation-inducing factor (Develop. Growth & Differ., 36(1), 1-8 (1994). However, nothing is known as to how MK functions on retinopathies.
Generally speaking, it has been demonstrated that one factor of cytokine exhibits a wide variety of physiological activities, while different factors of it exhibit similar physiological activities. When an attempt is made to apply these cytokine factors to clinical situations, undesirable actions frequently occur in reality instead of intended actions of cytokine. This exemplifies the difficulty in the clinical application of cytokine. Therefore, it is critically important for one who attempts a clinical trial of cytokine to be well aware of details of its biological actions.
Accordingly, a goal of the present invention is to clarify new physiological activities of MK that are not known previously and to pursue the applicability of MK as a medicine.
In view of the foregoing, the present inventors conducted research on the retinal degeneration inhibitory action of MK using animals under conditions of constant light so as to clarify new physiological activities of MK that have formerly been unknown. They tested bFGF in parallel, since bFGF exhibits analogous physiological activities, to clarify the difference in efficacy between MK and bFGF as well as effects that are considered to be an outcome of side reactions. As a result, MK, like bFGF, exhibited an inhibitory action against light-induced retinal degeneration. There was a difference between MK and bFGF in incidence of retinal macrophages, which was considered to be caused by a side reaction. The inventors found that MK was accompanied by a less degree of harmful side effects than bFGF, leading to completion of the invention.